The present invention generally relates to a method of extracting a feature from a line pattern and a line pattern recognition method using the same, and more particularly to a method of extracting a feature from a line pattern and a line pattern recognition method which are suitable for recognizing hand written patterns, such as hand written characters and hand written drawings, by an off-line process.
In hand written line patterns, such as hand written characters and hand written drawings, there are various pattern changes in a line pattern (a character) so that it is difficult to exactly recognize a hand written pattern by an off-line process.
Conventionally, a method of extracting a feature from a hand written line pattern and a line pattern recognition method, in which the contours of the line pattern or the background of the line pattern are analyzed, have been proposed. In such conventional methods, the analysis results are obtained by use of feature parameter vectors which strongly firmly depend on a determined coordinate system so that it is necessary to normalize a line pattern before analyzing. That is, it is necessary to convert a line pattern data indicated by a coordinate system into a data indicated by a predetermined normal coordinate system. Thus, if the normalization of the line pattern fails, the feature parameter vector is changed so that a recognition error and a rejection which indicates a state where it is impossible to recognize the line pattern occur.
In order to eliminate the disadvantage described above, a quasi-topological method has been proposed (SHUNJI MORI: A Non-Metric Model of Handprinted Characters, Transaction of the Institute of Electronics and Communication Engineers of Japan, Vol. J 62 - D , No. 10, pp. 641-646, Oct. 1979). In this quasi-topological method, the analysis results depend on only the directions of coordinate axes, and do not depend on coordinate values. Then, the background area structured by strokes (lines) is analyzed by use of a primitive sequence of a curve. However, the process of calculating the primitive sequence is complicated, and it is difficult to apply the calculation process to various primitive sequences. A concatenation between the primitive sequences is indefinite. In addition, the feature of the background of the line pattern inadequately corresponds to a user's visual sense so that it is difficult to recognize a hand written character whose shape has greatly changed.